Diameter of the Sun Activity (due as part of Quiz 1)
Brief Overview
of Activity: A pinhole can form an
image in much the same way
as a lens. Measuring the size of the Sun's projected image and the
distance
between the pinhole and the image, you will be able to calculate the
diameter
of the Sun.
Required Items: a friend to help you, a broom handle (or mop handle or long straight piece of wood of similar dimensions), a ruler (marked in centimeters), two envelopes (or two 5 x 7 index cards), a pencil, masking tape, one stickpin.
Number
of Observations needed: 1
Timing
of Observations: near noon on a bright
sunny day
Procedure:
Preparation: Use the stickpin to poke a small hole near the center of one of the envelopes. Mark a location near the top of the broom handle with masking tape (this is where your friend will hold the envelope with the pin-hole). Mark another location near the end of the broom handle with masking tape (this is where you will observe and mark the image). Carefully measure the distance between your two marked locations on your broom handle. Make your measurement to the nearest 0.1 centimeter and record here: D = ___________ cm.
Observation: Caution: never stare directly at the Sun. Gather
your friend, marked broom handle, two envelopes, pencil, and then head
outside.
With your friend holding the envelope with the pinhole at the upper
marked
position and you holding the other envelope at the lower marked
location, align
the broom handle such that a small faint image of the Sun's disk is
seen on the
lower envelope. You may find it convenient to actually sit on the
ground for
this procedure. With a pencil, carefully mark the location of opposite
sides of
the Sun's disk. Below is a diagram of the setup.
Calculation: From your marked envelope, carefully measure the size of the projected image of the Sun's disk to the nearest 0.1 centimeter and record here: d = __________ cm.
Next, use the
relationship below to calculate the
Sun's diameter in kilometers. Note that the distance to the Sun is 1.5
x 10
8 km.
Sun's diameter in kilometers image diameter in centimeters d
----------------------------------- = ------------------------------------------- = ---
Distance to the Sun in kilometers distance between image and pinhole in cm D
Record your calculated
value for the diameter of
the Sun ______________________ km